1. Technical Field of the Invention
This invention generally relates to the field of communication systems and, more particularly, to a Voice over Digital Subscriber Line (VoDSL) gateway to gateway communication system for use in the Public Switch Telephone Network (PSTN).
2. Description of the Background Art
Digital Subscriber Line (DSL) is a technology that enables simultaneous voice and data communication via a single transmission medium, such as a conditioned copper pair. DSL also provides a relatively high data rate for such data communications. Traditionally, if a subscriber wanted to receive and transmit voice and data simultaneously, or to have more than one voice line, the subscriber required more than one telephone line such additional telephone lines depended upon the availability of extra copper pairs being available from the local service provider""s Central Office (CO) to the subscriber""s business or home. With the advent of DSL, an additional telephone line is no longer required since DSL technology allows the simultaneous operation of a plurality of telephones and/or at least one data device over a single copper pair.
In providing VoDSL service, the convention is to digitize and compress, at the subscriber""s premise, one or more voice inputs from respective telephones using a conventional voice compression algorithm. The compressed voice traffic is then multiplexed with any data traffic. The multiplexed voice and data traffic is then packetized into an Asynchronous Transfer Mode (ATM), Internet Protocol (IP) or frame relay format to be transmitted over a copper loop (or other medium) using DSL. At the CO, a Digital Subscriber Line Access Multiplexer (DSLAM), operates as a packet concentrator to multiplex a number of packetized voice/data signals and send the multiplexed signals to a VoDSL gateway, where the voice traffic is decompressed and converted to standard 64kb/s signals using Pulse Code Modulation (PCM). The VoDSL gateway interfaces with the Public Switch Telephone Network (PSTN) using typically the Bell Communications Research""s Generic Requirements GR-303 or Technical Requirements TR008 protocol, and the PCM signal will be sent through the PSTN using Time Division Multiplexing (TDM) via Digital Signal level Zero (DS0) channels on a trunk, also known as a T1.
After being routed through the PSTN, the voice traffic is provided to a second VoDSL gateway that operates to compress, multiplex and packetize the received 64kb/s DS0 signal. The resulting signal is then transmitted to the subscriber""s premises where the voice traffic will be decompressed, demultiplexed, depacketized and undigitized again.
The invention comprises a system and method for transmitting and receiving VoDSL voice traffic that avoids, where possible, the transcoding of a speech signal multiple times. The invention advantageously provides enhanced Quality of Service (QoS) by opportunistically avoiding signal degradation.
A method for routing voice traffic using a Public Switch Telephone Network (PSTN) according to the invention comprises the steps of: receiving, at a VoDSL gateway servicing a first subscriber, compressed voice traffic from the first subscriber for routing to a second subscriber; determining whether the second subscriber is served by a respective second VoDSL gateway; processing the received voice traffic in a manner dependent on whether the second subscriber is served by the respective second VoDSL gateway; and communicating with the second subscriber.
A gateway to gateway communication system according to the invention comprises: a Voice over Digital Subscriber Line (VoDSL) gateway, for communicating voice traffic between a first subscriber and a second subscriber via a Public Switch Telephone Network (PSTN); the VoDSL gateway, in response to a second VoDSL gateway communicating a signaling message via the PSTN, transmits the voice traffic in a transport packet to the second VoDSL gateway; and the VoDSL gateway, in response to a failure to detect the second VoDSL gateway, encoding and transmitting the voice traffic to the second subscriber.